Cryogenic liquid storage apparatus



Jan. 17, 1967 A J. H T

CRYOGENIC LIQUID STORAGE APPARATUS 2 Sheets-Sheet 1 Original Filed Dec.

INVENTOR AUSTIN J SHORT 2 ATTORNEY Jan. 17, 1967 J SHORT CRYOGENIC LIQUID STORAGE APPARATUS 2 Sheets-Sheet 2 Original Filed Dec. 29, 1964 IN'VENTOR AUSTINI J. SHORT ATTORNEY United States Patent ()fitice 3,298,187 CRYOGENIC LIQUID STORAGE APPARATUS Austin J. Short, Kenmore, N.Y., assignor to Union Carbide Corporation, a corporation of New York Continuation t application Ser. No. 421,7?0, Dec. 29, 1964. This appiication Apr. 18, 1966, Ser. No. 549,112 9 Claims. (Cl. 6250) This application is a continuation of application Ser. No. 421,790 filed Dec. 29, 1964.

This invention relates to apparatus for storing lowboiling cryogenic liquids, and in particular to apparatus for controlling thermal oscillations in double-walled cryogenic liquid containers.

It is generally recognized by the prior art that many containers for storing low-boiling cryogenic liquids, principally liquid helium, may under certain conditions exhibit a pressure pulsation or oscillation condition which usually results in a substantial increase in the liquid evaporation rate from the container. Such oscillations apparently involve the rapid oscillation or periodic movement of colder gas from the vapor space over the liquid body towards the warm end portion of a liquid filldischarge conduit and back to the vapor space. As a result, atmospheric heat is pumped into the liquidstormg inner vessel thereby increasing the evaporation rate of the stored liquid. The oscillations appear to be induced spontaneously within a liquid filldischarge conduit under certain conditions of temperature, pressure and conduit geometry, and may occur in either gas phase or liquid phase conduits of either vertical or horizontal configuration. The driving force for such oscillations is probably the large temperature difference along the conduit; they appear to be thermally induced and are termed thermal oscillations. Of course such thermal oscillation conditions are very undesirable even in minor form, and severe oscillations are intolerable. The oscillations may reach proportions which result in total loss of container contents in a few hours.

An object of this invention is to provide improved cryogenic storage apparatus with means for controlling and minimizing thermal oscillations. Other objects and advantages will be apparent from the ensuing disclosure and appended claims.

In the drawings, FIG. 1 is a schematic view taken in cross-sectional elevation of apparatus constructed according to this invention.

FIG. 2 is a schematic view taken in cross-sectional elevation of apparatus similar to the FIG. 1 embodiment but also including a removable liquid transfer tube.

According to one embodiment, cryogenic liquid storage apparatus is provided including a double-walled container having an inner vessel and an outer casing with an evacuable thermal insulating space therebetween. An outer vapor chamber portion of the container is gastightly connected to the outer casing upper surface. Vapor conduit means extend from this outer vapor chamber through the outer casing and inner vessel walls with an inner end terminating in the upper portion of the inner vessel and an outer end terminating in the vapor chamber. A thermal oscillation damper chamber of greater than 5 cubic centimeters volume is located outside the inner vessel and vapor flow restricting conduit means are provided with one end connected to the vapor chamber and the other end connected to the damper chamber. The last mentioned conduit has a lengthtoinner effective diameter ratio of at least 52 and an effective diameter of at least ;-inch. Also, the damper chamber has an internal transverse length of at least 2 times the inner effective diameter of the conduit, and a larger volume than the container outer vapor chamber portion.

3,29%,l87 Patented Jan. 17, 1957 As used herein, the term outer vapor chamber portion of the container includes the upstream part of the internal volume of any over-pressure relief devices directly connected with such chamber. For example, if a safety valve is so connected the outer vapor chamber portion includes the pressurized internal gas volume part of such valve located upstream of the valve seat.

I have unexpectedly discovered that thermal oscillations of cryogenic containers are either greatly suppressed or eliminated by a particular combination of flow restricting conduit minimum diameter, flow restricting conduit length-to-inner effective diameter minimum ratio, damper chamber minimum volume and "volume relationship to the container outer vapor chamber portion. The damper chamber by itself without a restriction portion incorporated therewith will not suppress the thermal oscillations. Moreover, combinations of flow restrictions and damper chambers outside the scope of this invention do not effectively mitigate the oscillations. For example, excessively large diameter conduits of short length produce thermal oscillations as severe or worse than the original system without the conduit.

Thermal oscillations are the rapid transport of gas between areas or regions having different temperatures and pressures, through areas of a connecting volume or conduit. These pressure pulses of vapor result in the transport of heat to the cold area of the confined volume. In the case of liquid helium storage containers, the addition of heat to the cold area or liquid reservoir results in the excessive evaporation of stored liquid. The evaporation of liquid then causes an increase in gas pressure at the cold end. The cold gas then expands into the warm end area where its temperature increases and its pressure likewise increases. The gas again expands into the cold area thus completing the cycle to promote oscillation of the gas.

The novel apparatus of this invention may not completely eliminate the thermal oscillations but instead reduces them to such a low magnitude that the oscillations pump little if any appreciable heat into the liquid vessel. It is believed that the energy contained in the pressure pulse is expended in transporting the gas through the flow restricting conduit and in the compression of the gas in the damper chamber. The increased energy supplied to the gas in the damper chamber is not sufiicient to transport the warmed gas back through the flow restricting conduit to the vapor chamber in time to support the oscillation. With all variables constant, certain sized conduits (]ength-to-inner eifective diameter ratio) function more effectively than others, while conduits with L/D values of less than about 52 do not effectively suppress thermal oscillations. It is likely that the optimum restriction acts to return the pressure pulse to the inner vessel vapor space at the proper time in the cycle to act to decay the oscillation, i.e. produces a de-tuned system. Thus, no heat is pumped back into the cold region of the container. The result is the cycle is interrupted and the oscillation ceases. The potential to oscillate, however, is still present as evidenced by the fact that the system will oscillate the moment the external damper chamber volume is removed. If the L/D ratio is les than about 52, the conduit is not sufficiently restrictive to delay the pressure pulse return from the damping chamber and avoid amplification of the warm gas pressure pulse in the outer vapor chamber portion of the container. Moreover, the eflfective diameter of the flow restricting conduit must be at least -inch for an adequate quantity of warm gas to flow from the outer vapor chamber portion to the damping chamber and thus decay the pulse As used herein the term effective diameter includes conduits having non-circular cross-sectional areas, e.g. oval shape, which are equivalent 3 to the area of a circular conduit having a diameter of at least -inch.

Referring now to the FIG. 1 cryogenic liquid container 10 includes inner vessel 11 and outer casing 12. The intervening space 13 is evacuated to pressure below about 10 mm. Hg to minimize heat inleak from the atmosphere. Evacuable space '13 may be filled with a solid thermal insulating material as for example alternate layers of low conductive paper and radiation-impervious aluminum foil, as described in Matsch U.S. Patent No. 3,009,600 issued November 21, 1951. Alternatively the walls forming space 13 may be coated with a highly reflective surface as for example silver.

An elongated upper section 14 of container 10 having reduced cross-sectional area is open at its top end for access to inner vessel 11. Neck tube 15 is concentrically spaced within such section 14 and leak-tightly bonded at its lower end to the walls of hole 16 in the upper end of inner vessel 11. The upper end of neck tube 15 is leak-tightly joined to the top end of the container elongated section 14 for extension of the evacuable insulating space to such end. Neck tube 15 is preferably constructed of low conductive material such as stainless steel or a thermosetting phenol formaldehyde resin reinforced with paper. In the illustrated embodiment the primary function of neck tube 15 is to provide the aforementioned vapor conduit means extending through the outer casing and inner vessel walls with an inner end terminating in the upper portion of the inner vessel and an outer end terminating in the outer vapor chamber portion 17 of container 10. However, in this particular embodiment neck tube 15 also serves to support inner vessel 11 within outer casing 12. Additional vertical support means may be provided at the inner vessel lower end if desired. Lateral stabilization means for inner vessel 11 may also be used as will be understood by those skilled in the art.

Outer vapor chamber portion 17 is leak-tightly joined to the upper end of neck tube 15 and forms an extension thereof which may or may not be partially insulated. As previously indicated, outer vapor chamber portion 17 is the gas volume immediately adjacent to and in communication with the outer portion of neck tubegas conduit 15, and is confined by manifold piping and valve closures. Outer chamber portion 17 is normally at or near ambient temperature except during cryogenic liquid filling or during certain fluid withdrawal operations when it usually becomes quite cold from the increased quantity of cold vapor passing outwardly therethrough. Cryogenic liquid is changed into container 10 through fill conduit 18 having inlet valve 19 therein communicating with vapor chamber portion 17. The liquid flows through vapor conduit neck tube 15 and thence into inner vessel 11 for storage therein. The cryogenic liquid such as helium is stored at above-atmos-pheric pressure and if the storage period is sufl iciently long this pressure will build up due to heat inlea-k and evaporation. To avoid excessive pressure buildup, pressure relief means as for example relief valve 20 and bursting disk 21 are provided in vapor flow communication with vapor chamber portion 17 by conduit 22. Vapor may be discharged from container 10 as desired through discharge valve 23 in conduit 22. As previously indicated the term outer vapor chamber portion includes the internal volume of relief valve 20, bursting disk 21 and conduit 22 but not their external volume continguous to the surrounding atmosphere.

Vapor flow restricting conduit 24 having a length-toinner effective diameter ratio of at least 52 is provided with one end leak-tightly connected to outer vapor chamber portion 1'7 and the other end similarly connected to damper chamber 25. This chamber may be provided with vent valve 26 and has a volume of at least cubic centitmeters, the volume also being larger than that of outer vapor chamber portion 17. Damper chamber 25 furthermore has an internal dimension a measured normal 4 to the conduit 24 axis b-b of at least 2 times the inner diameter of this conduit.

During storage of cryogenic liquid, cold vapor is formed in the upper end of inner vessel '11 by evaporation. The evaporation of liquid then causes a gradual increase in gas pressure over the liquid. The cold gas expands into warm-outer vapor chamber portion 17 causing a temperature and pressure increase in that region. The gas then expands backwardly into the colder inner vessel 11 and without this invention the cycle is repeated to establish a thermally induced oscillation. However, in the present apparatus the thermal oscillation is controlled because the pressure pulse in outer chamber portion 17 also flows as a pressure pulse through vapor flow restricting conduit 24 and is slightly compressed in damper chamber 25. The damping chamber 25 must have an internal transverse length of at least twice the effective diameter of flow restricting conduit 24 to provide the necessary mixing and fluid friction of the emerging pressure pulse vapor. The vapor in chamber 25 does not contain sufficient energy to produce backward flow through conduit 24 in time to support a pulsating flow of warmed vapor back into the inner vessel. Accordingly the initial thermal oscillation is not reinforced, the cycle is interrupted and the oscillation decays.

It has been previously indicated that the volume of damping chamber 25 must be at least 5 cubic centimeters and at least as large as the volume of outer vapor chamber portion 17. Smaller damping chambers do not introduce sufiicient time lag in the pressure pulse returning through flow restricting conduit 24 to avoid amplifying the pulse remaining in vapor chamber 17.

If desired a secondary vapor passageway may be provided in neck tube 15 so that if the primary vapor passage ever inadvertently becomes plugged with ice or solid air the other passage will be open to safely relieve gas pressure within the container 10. This secondary vapor passageway may take the form of a low conductive metal or plastic tube 27 preferably concentrically positioned inside neck tube 15 and sized so as to provide an annular space 23 therebetween. The upper end of secondary vapor passageway 27 is fitted with relief valve 29 and joins with liquid fill conduit 18 through valve 19 and also with secondary vapor flow restricting conduit 30 sized on the same basis as primary vapor flow restricting conduit 24. The opposite end of conduit 30 connects with secondary damper chamber 31, also sized on the same basis as primary damper chamber 25 and provided with vent valve 32. The outer vapor chamber portion of the secondary vapor path comprises that portion of tube 27 which extends outside the elongated portion of outer casing 14 surrounding neck tube 15, as well as the upstream or inside portions of liquid fill valve '19 and relief valve 29.

During normal operation secondary vapor passageway 27 is closed and the vapor from inner vessel 11 flows through annular space 28 to outer vapor chamber portion 17 and then through primary conduit 22 to discharge valve 23. In the event that annular space 28 becomes plugged wit-h solid ice, the pressurized vapor vents through relief valve 29. It is possible for warmed gas to be vented through flow restriction conduit 24 to primary damping chamber 25 and valve 26, or through conduit 30 to secondary damping chamber 31 and vent valve 32. However, this is not the preferred venting sequence and the damping chambers 25 and 31 are usually dead-ended.

FIG. 2 illustrates another cryogenic liquid storage apparatus constructed according to the present invention. This apparatus is similar to that previously described and shown in FIG. 1, but differs mainly in the use of a removable liquid transfer conduit assembly 35. This assembly is used to both introduce cryogenic liquid into inner vessel 11 and withdraw liquid therefrom. The assembly 35 is inserted for either operation through wideopening valve 36 such as the ball or gate type, and the inner end extends to a point near the bottom of inner vessel 11. A pressure seal is provided between the inner wall of ball valve 36 and the outer wall of liquid transfer conduit assembly 35 by seal ring 37.

Assembly 35 includes inner liquid conduit 33 preferably concentrically positioned within outer conduit 39 with appropriate sealing means therebetween to provide an annular vaccum insulating space 40 thereby minimizing atmospheric heat inleak. The vacuum insulating space 40 is particularly effective in achieving low evaporation losses during liquid transfers and may include shut off valve 41 at its upper end. When liquid transfer conduit assembly 35 is not needed it may be withdrawn through neck tube 15, outer vapor chamber portion 17, and ball valve 36 closed.

It will be noted that the FIG. 2 assembly does not include a secondary vapor relief path as does the FIG. 1 embodiment, so that a secondary flow restricting conduit and damping chamber are not required. The outer vapor chamber portion 17 of the FIG. 2 container comprises the inside volume of neck tube above the reduced diameter section 42 of the container vacuum insulating jacket, the volume below slidable ring seal 37, conduit 22 and the upstream volume of relief valve and bursting disk 21. Vapor flow restricting conduit 24 is c011- nected at one end to outer vapor chamber portion 17 of container 10 and at the other end to damping chamber 25. If desired, liquid transfer conduit assembly 35 may also be used with containers having a secondary relief in the neck tube and extended /z-inch below the latter as illustrated in FIG. 1. This inner tube was formed of a thermosetting phenol formaldehyde resin reinforced with paper. Significant thermal oscillations resulted from the introduction of the secondary vapor relief path, to the extent that the net evaporation rate increased to an intolerable value estimated to exceed 10% capacity loss per day. Both a primary damping assembly comprising conduit 24 and chamber 25, and a secondary damping assembly of conduit and chamber 31 were installed, and certain combinations were successful in suppressing thermal oscillation so that the net evaporation rate returned to about 1.0% capacity loss per day. It was also found that the primary and secondary damping chambers 25 and 31 could be cooled to at least 77 C. and heated to at least 135 C. without effecting their efficiencies in suppressing thermal oscillations. Certain other combinations of flow restricting conduit and damping chambers were not successful in suppressing thermal oscillation. The A -inch diameter flow restricting tube tests differed from the larger tube tests in that a Ai-inch ID. x %-inch O.D. vacuum insulated liquid transfer conduit was inserted through an open ball valve and the neck tube to a position near the bottom of the inner vessel. Thermal oscillation occurred in the liquid transfer conduit, and flow restricting tube-damping chamber assemblies were attached to the A-inch inner tube of this conduit. The data from the Example I tests is summarized in Table A.

Table A THERMAL OSCILLATION WITH 110 LIIER LIQUID HELIUM CONTAINER Outer Vapor Damping L (restricting Thermal Flow Restricting Tube Chamber Chamber tube length) ID Oscillation Portion Volume (co) (restricting Elnuated Volume (00.) tube diameter) 0.065 ID ($111) 1; 1% long. 5 25 23 No. 0005 ID (110) x 3 long 5 25 46 Yes 0.005 ID (%s) x 8-10 101 5 25 123 Yes 0150 ID x 2 long 375 1, 000 133 Yes. 0 210 ID x 361ong 40 700 171 Yes 0 210 ID x 41" lon 375 1,000 195 Yes. 0.250 ID x 15-20 1011 375 1,000 60-80 Yes. 0.3125 ID AM) x 1 long 40 330 3. 2 No. 0. 25 ID (940) x 11 long 375 1, 000 35 No. 0. 25 A x 14 long 375 l, 000 45 N0. 0. 375 1,000 51 N0. 0. 375 1, 000 (57 Yes 0. 375 1,000 34 N0. 0 375 1,000 40 No. 0 375 1, 000 48 N 0.

EXAMPLE II passage similar to the FIG. 1 construction, as by inserting the assembly through wide-opening valve 17 and inner or secondary tube 27.

The advantages of the present invention were clearly demonstrated in a series of tests with double-walled containers storing liquid helium and constructed similar to the illustrated embodiments. In these tests, thermal oscillations were detected in several ways, depending on their severity. In some cases they were severe enough to be detected audibly as by container humming (a low-pitched whistle), visually as by fluctuation of a pressure gage needle or manometer level, or by manual feel such as vi bration of rubber hose walls. In other cases thermal oscillations were of lower magnitude and detectable only by evaporation rate test such as when the observed evaporation rate exceeded the usual or expected range for the particular type container. In each test thermal oscillation was considered eleminated only if the pressure pulses were damped immediately, i.e. within one minute.

EXAMPLE I A liquid helium container with a liquid helium storage capacity of about 110 liters demonstrated a net evaporation rate of 1.0% of capacity loss per day. There were no noticeable thermal oscillations. However, because of the aforedescribed danger of ice-solid air accumulation in the 14-inch outside diameter (OD) x 0.015-incl1 wall thickness neck tube, a secondary vapor relief path in the form of a 5-inch OD. x /z-inch I.D. tube was suspended A container with liquid helium storage capacity of about 25 liters and having a secondary vapor relief path exhibited a liquid helium evaporation initial rate of about 2.0% loss per day as received from the helium charging plant. The next morning the rate had increased to about 8.2% loss per day. Thermal oscillations were obviously present as considerable vibration was noted. The addition of certain primary and secondary damping assemblies to the vapor relief paths immediately stopped the oscillations and the helium evaporation rate dropped sharply. The net evaporation rate with the damping assemblies attached was about 1.2% loss per day. The data from the Example 11 tests is summarized in Table B.

An inspection of Tables A and B reveals that when the ratio of the flow restricting conduit length to the flow restricting conduit diameter is below about 52, the thermal oscillations are not damped. For example, in the liter container tests using a -inch I.D. tube, a 16-inch long section having an L/D value of 51 was ineffective whereas a 21-inch long section was very successful in suppressing thermal oscillation. Although the reasons for this phenomenon are not fully understood a probable explanation is that the shorter tube did not offer sufficient restriction to the pressure pulse for avoiding amplification of the remaining part of the original pulse or a subsequent pulse in the outer vapor chamber portion by 7 the pulse segment returning from the damping chamber through the tube.

Based on the aforeclescribed tests the vapor fiow restricting conduit preferably has an effective inner diameter being joined to liquid filling control valve means as a second outer vapor chamber portion; a second thermal oscillation damper chamber outside said inner vessel of greater than cubic centimeters volume and also having of 0.15-inch to 0.25-inch and an L/D ratio of between 5 larger volume than said second outer vapor chamber about 100 to 400. The damper chamber preferably has portion; and second vapor flow restricting conduit means a volume of between about 20 and 2000 cubic centimeters. having one end joined to said second outer vapor cham- Although particular embodiments of this invention have ber portion and the other end joined to said second been described in detail, it is contemplated that modidamper chamber, said second vapor flow restricting confications of the apparatus may be made and that some duit means having a length-to-inner effective diameter features may be employed without others, all within the ratio of at least 52, an effective diameter of at least SCOPe the lnventwninch, and said second damper chamber having an inter- P P P G the Vapor condult lolnlng the cryogemc nal transverse length of at least 2 times the inner effective liquid storing inner vessel and the outer vapor chambei diameter of the Second Vapor flow restricting conduit need not form part of the support system of this vessel; 5 means thls condult. may be enilmly separate.from F support 3. Cryogenic liquid storage apparatus according to means and in a non-straight configuration. Similarly the L claim 1 including an inseriable and removable liquid vapor flow restricting conduit may be in the form of bent tnnsfer conduit slideqbl and as ti hLl extend. or coiled tubing and may extend inside the damper chamh t y h g i y d ber instead of terminating at the walls of such chamber. mug Sm Ou er vapor c er Portion an Sal AS another Variation the damper chamber may be vapor conduit means to a position ad acent the lower cated Within the evacuable thermal insulating space sep- 6nd of 531d l arating the inner vessel and the outer casing, instead of cryogelllc llquld Storagfi apparatus accordll'lg to external to the entire container as illustrated in FIGS. 1 01mm 1 lllcludlng a Wide Openlng liquid fill Valve and 2. In this arrangement the flow restricting conduit .1: nected to said outer vapor chamber portion of the coninay extend into the same evacuable space. tainer.

Table B THERMAL OSCILLATION WITH LITER LIQUID HELIUM CONTAINER Outer Vapor Damping L (restricting Thermal Flow Restricting Tube Chamber Chamber tube longth)/D Oscillation Portion Volume (cc.) (restricting Elimated Volume (00.) tube diameter) 0.125 ID x 20 long l, 000 1, 000 160 Yes 0.125 ID x long 1, 000 1,000 320 Yes 0.125 ID x 70 long. l, 000 1, 000 560 No. 0.125 ID x 8 long plus 0.025 ID x 3 long. 1,000 1,000 70 Yes 0.125 ID x 2 long plus 0250 ID x 5 1O1lgw l, 000 1,000 36 No. 0.210 ID x 23 long 20 700 110 Yes 0.210 ID x 23 long- 2s 1, 000 110 Yes 0.210 ID x 23 long. 100 1, 000 110 Yes 0.250 ID x 20 long. 20 700 80 Yes 0250 ID x 20 long- 100 1,000 80 Yes 0.250" ID X 22 long 100 1,000 $3 Yes What is claimed is:

1. Cryogenic liquid storage apparatus comprising a double-walled container having an inner vessel and an outer casing with an evacuable thermal insulating space therebetween, and an outer vapor chamber portion of said container being gas-tightly connected to the outer casing; vapor conduit means extending through the outer casing and inner vessel walls with an inner end terminating in the upper portion of said inner vessel and an outer end terminating in the container outer vapor chamber portion; a thermal oscillation damper chamber outside said inner vessel of greater than 5 cubic centimeters volume and also having larger volume than said container outer vapor chamber portion; and vapor flow restricting conduit means having one end joined to said container outer vapor chamber portion and the other end joined to said damper chamber, said vapor flow restricting conduit means having a length-to-inner effective diameter ratio of at least 52 and effective diameter of at least -inch, and said damper chamber having an internal transverse length of at least 2 times the inner effective diameter of the conduit.

2. Cryogenic liquid storage apparatus according to claim 1 including secondary vapor conduit means within said vapor conduit means and of sufliciently smaller effective diameter to provide an annular space therebetween, said secondary vapor conduit means also extending through the outer casing and inner vessel walls with an inner end terminating in the upper portion of said inner vessel and the outer end extending through said outer vapor chamber portion of said container and 5. Cryogenic liquid storage apparatus according to claim 1 including a Wide opening liquid fill valve connected to said outer vapor chamber portion of the container, and an insertable and removable liquid transfer conduit slidably and gas-tightly extending consecutively through said liquid fill valve, said outer vapor chamber portion and said vapor conduit means to a position adjacent the lower end of said inner vessel.

6. Cryogenic liquid storage apparatus according to claim it in which the effective diameter of said vapor flow restricting conduit is between about 0.15' inch and 0.25 inch, the length-to-effective diameter ratio of such conduit is between about and 400 and the volume of said damper chamber is between about 20 and 2000 cubic centimeters.

7. Cryogenic liquid storage apparatus comprising a double-walled container having an inner vessel and an outer casing with an evacuable thermal insulating space therebetween; fluid conduit means extending through the outer casing and inner vessel walls with an inner end terminating in said inner vessel; a thermal oscillation damper chamber outside said inner vessel of greater than 5 cubic centimeters volume; and fluid flow restricting conduit means having one end joined to said fluid conduit means outside said inner vessel and the other end joined to said damper chamber, said fluid flow restricting conduit means having a length-to-inner effective diameter ratio of at least 52 and efiective diameter of at least -inch, and said damper chamber having an internal transverse length of at least 2 times the inner effective diameter of the conduit.

3,298,187 9 10 8. Cryogenic liquid storage apparatus according to 2,968,161 1/1961 Bliss.

claim 7 wherein the inner end of said fluid conduit 3,201,946 8/1965 Paulinkanis. means terminates near the bottom of said inner vessel.

9. Cryogenic liquid storage apparatus according to FOREIGN PATENTS claim 7 wherein the inner end of said fluid conduit 5 12 677/33 3/1934 Australia means terminates near the top of said inner vessel.

References Cited by the Applicant OTHER REFERENCES UNITED STATES PATENTS Advances in Cryogenic Engineering, volume 1, pages 10 138-143 and 302-306, Plenum Press, Inc., NY. (1960). 2,396,459 3/1946 Dana.

2,502,588 4/1950 Preston et al. LLOYD L. KING, Primary Examiner. 

1. CROGENIC LIQUID STORAGE APPARATUS COMPRISING A DOUBLE-WALLED CONTAINER HAVING AN INNER VESSEL AND AN OUTER CASING WITH AN EVACUABLE THERMAL INSULATING SPACE THEREBETWEEN, AND AN OUTER VAPOR CHAMBER PORTION OF SAID CONTAINER GEING GAS-TIGHTLY CONNECTED TO THE OUTER CASING; VAPOR CONDUIT MEANS EXTENDING THROUGH THE OUTER CASING AND INNER VESSEL WALLS WITH AN INNER END TERMINATING IN THE UPPER PORTION OF SAID INNER VESSEL AND AN OUTER END TERMINATING IN THE CONTAINER OUTER VAPOR CHAMBER PORTION; A THERMAL OSCILLATION DAMPER CHAMBER OUTSIDE SAID INNER VESSEL OF GREATER THAN 5 CUBIC CENTIMETERS VOLUME AND ALSO HAVING LARGER VOLUME THAN SAID CONTAINER OUTER VAPOR CHAMBER PORTION; AND VAPOR FLOW RE STRICTING CONDUIT MEANS HAVING ONE END JOINED TO SAID CONTAINER OUTER VAPOR CHAMBER PORTION AND THE OTHER END JOINED TO SAID DAMPER CHAMBER, SAID VAPOR FLOW RESTRICTING CONDUIT MEANS HAVING A LENGTH-TO-INNER EFFECTIVE DIAMETER RATIO OF AT LEAST 52 AND EFFECTIVE DIAMETER OF AT LEAST 1/16-INCH, AND SAID DAMPER CHAMBER HAVING AN INTERNAL TRANSVERSE LENGTH OF AT LEAST 2 TIMES THE INNER EFFECTIVE DIAMETER OF THE CONDUIT. 